1,060 research outputs found
Adiabatic Connection for Strictly-Correlated Electrons
Modern density functional theory (DFT) calculations employ the Kohn-Sham (KS)
system of non-interacting electrons as a reference, with all complications
buried in the exchange-correlation energy (Exc). The adiabatic connection
formula gives an exact expression for Exc. We consider DFT calculations that
instead employ a reference of strictly-correlated electrons. We define a
"decorrelation energy" that relates this reference to the real system, and
derive the corresponding adiabatic connection formula. We illustrate this
theory in three situations, namely the uniform electron gas, Hooke's atom, and
the stretched hydrogen molecule. The adiabatic connection for
strictly-correlated electrons provides an alternative perspective for
understanding density functional theory and constructing approximate
functionals.Comment: 4 figures, has been published in J. Chem. Phy
Reliable energy level alignment at physisorbed molecule-metal interfaces from density functional theory.
A key quantity for molecule-metal interfaces is the energy level alignment of molecular electronic states with the metallic Fermi level. We develop and apply an efficient theoretical method, based on density functional theory (DFT) that can yield quantitatively accurate energy level alignment information for physisorbed metal-molecule interfaces. The method builds on the "DFT+Σ" approach, grounded in many-body perturbation theory, which introduces an approximate electron self-energy that corrects the level alignment obtained from conventional DFT for missing exchange and correlation effects associated with the gas-phase molecule and substrate polarization. Here, we extend the DFT+Σ approach in two important ways: first, we employ optimally tuned range-separated hybrid functionals to compute the gas-phase term, rather than rely on GW or total energy differences as in prior work; second, we use a nonclassical DFT-determined image-charge plane of the metallic surface to compute the substrate polarization term, rather than the classical DFT-derived image plane used previously. We validate this new approach by a detailed comparison with experimental and theoretical reference data for several prototypical molecule-metal interfaces, where excellent agreement with experiment is achieved: benzene on graphite (0001), and 1,4-benzenediamine, Cu-phthalocyanine, and 3,4,9,10-perylene-tetracarboxylic-dianhydride on Au(111). In particular, we show that the method correctly captures level alignment trends across chemical systems and that it retains its accuracy even for molecules for which conventional DFT suffers from severe self-interaction errors
Comparative Study of Covalent and van der Waals CdS Quantum Dot Assemblies from Many-Body Perturbation Theory
Quantum dot (QD) assemblies are nanostructured networks made from aggregates
of QDs and feature improved charge and energy transfer efficiencies compared to
discrete QDs. Using first-principles many-body perturbation theory, we
systematically compare the electronic and optical properties of two types of
CdS QD assemblies that have been experimentally investigated: QD gels, where
individual QDs are covalently connected via di- or poly-sulfide bonds, and QD
nanocrystals, where individual QDs are bound via van der Waals interactions.
Our work illustrates how the electronic, excitonic, and optical properties
evolve when discrete QDs are assembled into 1D, 2D, and 3D gels and
nanocrystals, as well as how the one-body and many-body interactions in these
systems impact the trends as the dimensionality of the assembly increases.
Furthermore, our work reveals the crucial role of the covalent di- or
poly-sulfide bonds in the localization of the excitons, which highlights the
difference between QD gels and QD nanocrystals.Comment: 25 pages, 4 figure
Adiabatic Connection in the Low-Density Limit
In density functional theory (DFT), the exchange-correlation functional can
be exactly expressed by the adiabatic connection integral. It has been noticed
that as lambda goes to infinity, the lambda^(-1) term in the expansion of
W(lambda) vanishes. We provide a simple but rigorous derivation to this exact
condition in this work. We propose a simple parametric form for the integrand,
satisfying this condition, and show that it is highly accurate for
weakly-correlated two-electron systems.Comment: 4 pages, 2 figures, submitted to Phys. Rev.
Energy Level Alignment at Molecule-Metal Interfaces from an Optimally-Tuned Range-Separated Hybrid Functional
The alignment of the frontier orbital energies of an adsorbed molecule with
the substrate Fermi level at metal-organic interfaces is a fundamental
observable of significant practical importance in nanoscience and beyond.
Typical density functional theory calculations, especially those using local
and semi-local functionals, often underestimate level alignment leading to
inaccurate electronic structure and charge transport properties. In this work,
we develop a new fully self-consistent predictive scheme to accurately compute
level alignment at certain classes of complex heterogeneous molecule-metal
interfaces based on optimally-tuned range-separated hybrid functionals.
Starting from a highly accurate description of the gas-phase electronic
structure, our method by construction captures important nonlocal surface
polarization effects via tuning of the long-range screened exchange in a
range-separated hybrid in a non-empirical and system-specific manner. We
implement this functional in a plane-wave code and apply it to several
physisorbed and chemisorbed molecule-metal interface systems. Our results are
in quantitative agreement with experiments, both the level alignment and work
function changes. Our approach constitutes a new practical scheme for accurate
and efficient calculations of the electronic structure of molecule-metal
interfaces.Comment: 15 pages, 8 figure
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